Berkeley Lab: Hybrid Ultra-Thin Perovskite: A Different Type of 2D Semiconductor


2D Perovskite Berkeley Peidong-image-2Berkeley Lab Researchers Produce First Ultrathin Sheets of Perovskite Hybrids

To the growing list of two-dimensional semiconductors, such as graphene, boron nitride, and molybdenum disulfide, whose unique electronic properties make them potential successors to silicon in future devices, you can now add hybrid organic-inorganic perovskites. However, unlike the other contenders, which are covalent semiconductors, these 2D hybrid perovskites are ionic materials, which gives them special properties of their own.
Researchers at the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have successfully grown atomically thin 2D sheets of organic-inorganic hybrid perovskites from solution. The ultrathin sheets are of high quality, large in area, and square-shaped. They also exhibited efficient photoluminescence, color-tunability, and a unique structural relaxation not found in covalent semiconductor sheets.
“We believe this is the first example of 2D atomically thin nanostructures made from ionic materials,” says Peidong Yang, a chemist with Berkeley Lab’s Materials Sciences Division and world authority on nanostructures, who first came up with the idea for this research some 20 years ago. “The results of our study open up opportunities for fundamental research on the synthesis and characterization of atomically thin 2D hybrid perovskites and introduces a new family of 2D solution-processed semiconductors for nanoscale optoelectronic devices, such as field effect transistors and photodetectors.”

(From left) Peidong Yang, Letian Dou, Andrew Wong and Yi Yu successfully followed up on research first proposed by Yang in 1994.

Yang, who also holds appointments with the University of California (UC) Berkeley and is a co-director of the Kavli Energy NanoScience Institute (Kavli-ENSI), is the corresponding author of a paper describing this research in the journal Science. The paper is titled “Atomically thin two-dimensional organic-inorganic hybrid perovskites.” The lead authors are Letian Dou, Andrew Wong and Yi Yu, all members of Yang’s research group. Other authors are Minliang Lai, Nikolay Kornienko, Samuel Eaton, Anthony Fu, Connor Bischak, Jie Ma, Tina Ding, Naomi Ginsberg, Lin-Wang Wang and Paul Alivisatos.
Traditional perovskites are typically metal-oxide materials that display a wide range of fascinating electromagnetic properties, including ferroelectricity and piezoelectricity, superconductivity and colossal magnetoresistance. In the past couple of years, organic-inorganic hybrid perovskites have been solution-processed into thin films or bulk crystals for photovoltaic devices that have reached a 20-percent power conversion efficiency. Separating these hybrid materials into individual, free-standing 2D sheets through such techniques as spin-coating, chemical vapor deposition, and mechanical exfoliation has met with limited success.
In 1994, while a PhD student at Harvard University, Yang proposed a method for preparing 2D hybrid perovskite nanostructures and tuning their electronic properties but never acted upon it. This past year, while preparing to move his office, he came upon the proposal and passed it on to co-lead author Dou, a post-doctoral student in his research group. Dou, working mainly with the other lead authors Wong and Yu, used Yang’s proposal to synthesize free-standing 2D sheets of CH3NH3PbI3, a hybrid perovskite made from a blend of lead, bromine, nitrogen, carbon and hydrogen atoms.

Structural illustration of a single layer of a 2D hybrid perovskite (C4H9NH3)2PbBr4), an ionic material with different properties than 2D covalent semiconductors.

“Unlike exfoliation and chemical vapor deposition methods, which normally produce relatively thick perovskite plates, we were able to grow uniform square-shaped 2D crystals on a flat substrate with high yield and excellent reproducibility,” says Dou. “We characterized the structure and composition of individual 2D crystals using a variety of techniques and found they have a slightly shifted band-edge emission that could be attributed to structural relaxation. A preliminary photoluminescence study indicates a band-edge emission at 453 nanometers, which is red-shifted slightly as compared to bulk crystals. This suggests that color-tuning could be achieved in these 2D hybrid perovskites by changing sheet thickness as well as composition via the synthesis of related materials.”
The well-defined geometry of these square-shaped 2D crystals is the mark of high quality crystallinity, and their large size should facilitate their integration into future devices.
“With our technique, vertical and lateral heterostructures can also be achieved,” Yang says. “This opens up new possibilities for the design of materials/devices on an atomic/molecular scale with distinctive new properties.”
This research was supported by DOE’s Office of Science. The characterization work was carried out at the Molecular Foundry’s National Center for Electron Microscopy, and at beamline 7.3.3 of the Advanced Light Source. Both the Molecular Foundry and the Advanced Light Source are DOE Office of Science User Facilities hosted at Berkeley Lab.
Advertisements

DOE: Berkeley Lab Awarded $8 Million for Hydrogen and Fuel Cell Research


Adam Weber and Jeffrey Urban at ALS SAXS/WAXS Beamline 7.3.3.

Adam Weber and Jeffrey Urban at ALS SAXS/WAXS Beamline 7.3.3.

New projects for hydrogen storage and fuel cell performance aim to bring down cost of fuel cell electric vehicles.

With commitments from leading car and stationary-power manufacturers to hydrogen and fuel cell technologies and the first ever fuel cell electric vehicle to go on sale later this year, interest is once again swelling in this carbon-free technology. Now, thanks to several new projects from the U.S. Department of Energy’s (DOE) Fuel Cell Technologies Office, scientists from Lawrence Berkeley National Laboratory (Berkeley Lab) will have an important role in accelerating innovation and commercialization of hydrogen and fuel cell technologies.

Berkeley Lab has been awarded $8 million for two new DOE research efforts, one to find new materials for hydrogen storage and another for optimizing fuel-cell performance and durability. In addition, Berkeley Lab is leading a range of other hydrogen and fuel cell research projects aimed at developing next-generation fuel cell and related energy-conversion technologies.

Adam Weber and Jeffrey Urban at ALS SAXS/WAXS Beamline 7.3.3.

“Berkeley Lab has had a strong fuel cell research program going back decades,” said scientist Adam Weber, who leads fuel cell research at Berkeley Lab. “With these new DOE consortiums, each national lab brings its core competences while synergistically leveraging each other. This way we’ll be able to push the state-of-the-art much faster and further than we could individually.”

Fuel cells are considered one of the most promising and fast-growing clean energy technologies. In 2014, about 50,000 fuel cell units were shipped worldwide, with a nearly 30 percent market growth every year since 2010. This year, Toyota’s Mirai will be the first fuel cell electric vehicle (FCEV) to be commercially available for sale in the U.S. Still, cost remains one of the biggest challenges to wider adoption.

The Fuel Cell—Consortium for Performance and Durability (FC-PAD) is led by Los Alamos National Laboratory and includes Argonne National Laboratory, Oak Ridge National Laboratory, and the National Renewable Energy Laboratory, with Weber serving as the consortium’s deputy director. Its goal is to improve and optimize polymer electrolyte membrane (PEM) fuel cells, which are used primarily for transportation, while reducing their cost. “If we can make individual cells more durable and perform better with less costly components or fewer of them, than you would drive down the cost of the vehicle,” Weber said.

Specifically one research focus of Weber’s work for FC-PAD will be trying to understand and optimize mass transport in the fuel cell, or the transport of reactants and products, such as hydrogen, oxygen, and water. Mass-transport issues can limit fuel-cell performance. “One of our core competences at Berkeley Lab is in mathematical modeling and advanced diagnostics, which we can use to study, explore, and describe the transport phenomena across length scales from the microstructural to macroscopic levels,” he said.

Like batteries, fuel cells use a chemical reaction to produce electricity. However fuel cells don’t need to be recharged; rather, they will produce electricity as long as fuel is supplied. In the case of a hydrogen fuel cell, hydrogen is the fuel, and it’s stored in a tank connected to the fuel cell.

Safe and cost-effective hydrogen storage is another challenge for FCEVs, one that the other DOE consortium, Hydrogen Materials—Advanced Research Consortium (HyMARC), seeks to address. HyMARC is led by Sandia National Laboratories and also includes Lawrence Livermore National Laboratory.

Jeff Urban, the HyMARC lead scientist for Berkeley Lab, noted the Lab’s strengths: “Berkeley Lab brings to the consortium a combination of innovation in H2 storage materials, surface and interface science, controlled nanoscale synthesis, world-class user facilities for characterizing nanoscale materials, and predictive materials genome capabilities.”

Researchers have two goals for hydrogen storage—greater storage density at lower pressure. Greater density will allow for greater vehicle driving range while lower pressure improves safety as well as efficiency.

Urban and his group have come up with novel ways to synthesize nanoscale metal hydrides to achieve extremely high hydrogen storage capacity. Yet the kinetics, or rate of chemical reactions, is one of the main challenges with this material. “HyMARC will allow us to further probe solid-solid interfaces in metal hydrides and evaluate microstructural engineering as a pathway to improved kinetics,” he said. “The unique combination of expertise spanning these consortia gives us a peerless network of close collaboration to surmount the fundamental scientific barriers underpinning some of these sticky challenges.”

Both of these consortiums are funded by DOE’s Fuel Cell Technologies Office, part of the Office of Energy Efficiency and Renewable Energy, and follow a similar model, where the core team consisting of the national labs will serve as a resource to industry and later also collaborate on innovative projects with universities and companies.

Another research focus is in catalysts, the subject of a collaboration between Berkeley Lab materials scientist Peidong Yang and scientists at Argonne National Laboratory. Last year they reported discovery of a new class of bimetallic nanoframe catalysts using platinum and nickel that are significantly more efficient and far less expensive than the best platinum catalysts used in today’s fuel cells.

Finally Berkeley Lab last month joined several other national labs as well as dozens of companies and other institutions in signing onto H2USA, a public-private partnership whose mission is “is to address hurdles to establishing hydrogen fueling infrastructure, enabling the large scale adoption of fuel cell electric vehicles.” Infrastructure is one of the critical challenges to wider hydrogen technology adoption, and one in which California has made a strong commitment.

“I’m very bullish on hydrogen. It’s clean and carbon-free, and it’s definitely a very integral part of the future energy economy,” Weber said. “Is it a very near-term drop-in replacement technology? No, I think it’s a little bit longer term, although we have commercial products like the Mirai available today. Like any new technology we have to go down the cost and manufacturing curves. As we bring in new ideas, concepts, and materials, I think we can easily bring down the cost.”

# # #

Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit www.lbl.gov.

DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

<!–

–>

Updated:

Researchers Intoduce an Electric Field to Enhance Solar Cell Performance


 

Electrical Field pic1Researchers at the Kavli Energy Nanosciences Institute, the University of California at Berkeley and the Lawrence Berkeley National Lab, have succeeded in boosting the performance of a new type of solar cell by simply applying an electric field to it. The device (made of low cost zinc phosphide and graphene) is novel in its design in that it lacks a junction between the two p- and n-type semiconductors that make it up – which is a first. The cell might be ideal for use in areas where the intensity of sunlight changes a lot over the course of the year.

The device and experimental results

“Our solar cell does not need to be doped, nor does it require high-quality heterojunctions, which are challenging and expensive to fabricate,” says team member Oscar Vazquez-Mena. “Our work is a novel and promising approach for making photovoltaics with low-cost and abundant materials such as certain phosphides and sulphides that are easy to synthesize and which are environmentally friendly.”

Beside expensive light absorbers like silicon, there are semiconductors like zinc phosphide, copper zinc tin sulphide, cuprous oxide and iron sulphide that are much cheaper. However, for these materials to efficiently convert sunlight into energy, they need to be doped to form homojunctions, or require complementary emitter materials to form high-quality p-n heterojunctions.

A team led by Alex Zettl, Harry Atwater, Ali Javey and Michael Crommie has now overcome this problem by making a simple junction with graphene rather than a semiconductor. A voltage applied to a gate over the junction can tune the energy barrier between the graphene and an adjoining layer of zinc phosphide to boost how efficiently solar cells made from these materials convert light into energy.

The devices are relatively simple to fabricate, says Vazquez-Mena. “Jeff Bosco from Harry Atwater’s team at Caltech makes high-quality zinc phosphide films and in our lab at UC Berkeley, we are experts at growing graphene on copper substrates. Basically, we transfer the graphene from the copper onto the zinc phosphide film to form a graphene- zinc phosphide junction. We then add an insulator layer on top of the graphene, prepared by our colleagues in Ali Javey’s team, also at UC Berkeley. Finally we add a thin top gate to the structure.”

Barrier is like a dam

Conventional solar cells normally contain two bulk semiconductors, with their electrons at different energy levels. These semiconductors are brought into contact to form an electric barrier between them that separates the electrons from each side. “This barrier can be likened to the dam in a hydroelectric power plant that separates two reservoirs of water at different heights,” explains Vazquez-Mena. “In a solar cell, the electric charges are the water in the dam and we use energy from the Sun to make the charges jump over the barrier.”

In the new device, the researchers used a layer of graphene in place of one of the semiconductors and added a top gate to it. “Why? Because it is easy to control the energy level of electrons in graphene by doing this,” Vazquez-Mena tells nanotechweb.org. “Such a thing is difficult to do in a bulk semiconductor.”

The top gate can regulate the barrier between graphene and the zinc phosphide, needed for the solar cell to work, he adds. “This is critical for the performance of the device and allows us to optimize the energy extracted from it. Going back to the dam analogy, it is as if we would be controlling the height of the dam.”

The fact that we can manipulate the barrier height in this way means that, in principle, we could make graphene junctions with many other materials, he says.

Modifying the barrier

In bulk semiconductor solar cells, the barrier height depends on the intrinsic properties of the materials making up the barrier. So, once you put the materials together, there is not much you can do to change the barrier, explains Vazquez-Mena.

“Our device is very different in that we can modify this barrier by simply applying an electric field to the top gate and adjusting the strength of the field applied for different materials and light conditions to optimize energy conversion. Our device, which is just a basic graphene-zinc phosphide solar cell, normally has an efficiency of 1% without any applied gate voltage, but we have doubled this to 2% by increasing the gate voltage to 2V. We have thus been able to boost its performance beyond the intrinsic properties of the material it is made up of.”

This type of solar cell might be ideal in climes where the sunlight varies a lot, he says – thanks to the fact that we can adjust the barrier to optimize energy conversion.

The California researchers say that they are looking to improve the efficiency of their devices and improving the quality of the graphene-zinc phosphide junction so that it produces a higher photocurrent. “We also want to apply our technology to other low-cost and readily available materials,” says Vazquez-Mena. “For example, the device we have made can be improved by using graphene itself or a transparent conductor like indium-tin oxide as the top gate.”

The team, reporting its work in Nano Letters, says that it will also test copper zinc tin sulphide, cuprous oxides and copper sulphide. “These materials are less harmful to the environment compared with commonly used solar cell materials like cadmium telluride and are cheaper than pure silicon. We definitely have many ideas to try but we also hope that other research groups will be inspired by our experiments and develop similar strategies to keep improving the efficiencies of alternative photovoltaic materials.”

Genesis Nanotech Headlines Are Out!


Organ on a chip organx250Genesis Nanotech Headlines Are Out! Read All About It!

https://paper.li/GenesisNanoTech/1354215819#!headlines

Visit Our Website: www.genesisnanotech.com

Visit/ Post on Our Blog: https://genesisnanotech.wordpress.com

 

SUBCOMMITTE EXAMINES BREAKTHROUGH NANOTECHNOLOGY OPPORTUNITIES FOR AMERICA

Chairman Terry: “Nanotech is a true science race between the nations, and we should be encouraging the transition from research breakthroughs to commercial development.”

WASHINGTON, DCThe Subcommittee on Commerce, Manufacturing, and Trade, chaired by Rep. Lee Terry (R-NE), today held a hearing on:

“Nanotechnology: Understanding How Small Solutions Drive Big Innovation.”

 

 

electron-tomography

“Great Things from Small Things!” … We Couldn’t Agree More!

 

Quantum Dots may turn House Windows into Solar Panels


 

New-QD-Solar-Cell-id35756-150x150A house window that doubles as a solar panel could be on the horizon, thanks to recent quantum-dot work by researchers at Los Alamos National Laboratory in the US in collaboration with scientists from University of Milano-Bicocca (UNIMIB) in Italy.

Their work, published earlier this year in Nature Photonics, demonstrates that superior light-emitting properties of quantum dots can be applied in solar energy by helping more efficiently harvest sunlight.

“The key accomplishment is the demonstration of large-area luminescent solar concentrators that use a new generation of specially engineered quantum dots,” said lead researcher Victor Klimov of the Center for Advanced Solar Photophysics at Los Alamos. Quantum dots are ultra-small bits of semiconductor matter that can be synthesized with nearly atomic precision via modern methods of colloidal chemistry.

A luminescent solar concentrator (LSC) is a photon-management device, representing a slab of transparent material that contains highly efficient emitters such as dye molecules or quantum dots. Sunlight absorbed in the slab is re-radiated at longer wavelengths and guided toward the slab edge equipped with a solar cell.

Quantum dots are embedded in the plastic matrix and capture sunlight to improve solar-panel efficiency.
Courtesy Los Alamos Lab.
 
LUMINESCENT SOLAR CONCENTRATOR AS LIGHT HARVESTER

Sergio Brovelli, a faculty member at UNIMIB and a co-author of the paper, explained, “The LSC serves as a light-harvesting antenna which concentrates solar radiation collected from a large area onto a much smaller solar cell, and this increases its power output. LSCs are especially attractive because in addition to gains in efficiency, they can enable new interesting concepts such as photovoltaic windows that can transform house facades into large-area energy-generation units.”

Because of highly efficient, color-tunable emission and solution processability, quantum dots are attractive materials for use in inexpensive, large-area LSCs. To overcome a nagging problem of light reabsorption, the Los Alamos and UNIMIB researchers developed LSCs based on quantum dots with artificially induced large separation between emission and absorption bands, known as a large Stokes shift.

These “Stokes-shift-engineered” quantum dots represent cadmium selenide/cadmium sulfide (CdSe/CdS) structures in which light absorption is dominated by an ultra-thick outer shell of CdS, while emission occurs from the inner core of a narrower-gap CdSe.

Los Alamos researchers created a series of thick-shell (so-called “giant”) CdSe/CdS quantum dots, which were incorporated by their Italian partners into large slabs (sized in tens of centimeters across) of polymethylmethacrylate. While being large by quantum dot standards, the active particles are still tiny, only about hundred angstroms across.

QUANTUM DOTS USED FOR NEW DISPLAYS

Quantum dots are ultra-small bits of semiconductor matter that can be synthesized with nearly atomic precision via modern methods of colloidal chemistry.

Their emission color can be tuned by simply varying their dimensions. Color tunability is combined with high emission efficiencies approaching 100%.3D Printing dots-2

These properties have recently become the basis of a new technology — quantum-dot displays — employed, for example, in the newest generation of the Kindle Fire e-reader.

In a new SPIE.TV video, Lawrence Berkeley National Lab director Paul Alivisatos demonstrates the Kindle Fire quantum-dot display.

 

DOI: 10.1117/2.4201407.10

Breakthrough Method (Discovery) for Characterizing Hot Carriers Could Hold the Key to Future Solar Cell Efficiencies


XBD200209-00526-02.PSDOne of the major road blocks to the design and development of new, more efficient solar cells may have been cleared. Researchers with the Lawrence Berkeley National Laboratory (Berkeley Lab) have developed the first ab initio method – meaning a theoretical model free of adjustable or empirical parameters – for characterizing the properties of “hot carriers” in semiconductors. Hot carriers are electrical charge carriers – electrons and holes – with significantly higher energy than charge carriers at thermal equilibrium.

“Hot carrier thermalization is a major source of efficiency loss in solar cells, but because of the sub-picosecond time scale and complex physics involved, characterization of hot carriers has long been a challenge even for the simplest materials,” says Steven Louie, a theoretical physicist and senior faculty scientist with Berkeley Lab’s Materials Sciences Division (MSD). “Our work is the first ab initio calculation of the key quantities of interest for hot carriers – lifetime, which tells us how long it takes for hot carriers to lose energy, and the mean free path, which tells us how far the hot carriers can travel before losing their energy.”

XBD200209-00526-02.PSD

A new and better way to study “hot” carriers in semiconductors, a major source of efficiency loss in solar cells, has been developed by scientists at Berkeley Lab. (Photo by Roy Kaltschmidt)

All previous theoretical methods for computing these values required empirical parameters extracted from transport or optical measurements of high quality samples, a requirement that among the notable semiconductor materials has only been achieved for silicon and gallium arsenide. The ab initio method developed by Louie and Jeff Neaton, Director of the Molecular Foundry, a U.S. Department of Energy (DOE) Nanoscience User Facility hosted at Berkeley Lab, working with Marco Bernardi, Derek Vigil-Fowler and Johannes Lischner, requires no experimental parameters other than the structure of the material.

(From left) Steve Louie, Marco Bernardi, Jeff Neaton and Johannes Lischner developed the first ab initio method for characterizing hot carriers in semiconductors. (Photo by Roy Kaltschmidt)

“This means that we can study hot carriers in a variety of surfaces, nanostructures, and materials, such as inorganic and organic crystals, without relying on existing experiments,” says Neaton. “We can even study materials that have not yet been synthesized. Since we can access structures that are ideal and defect-free with our methods, we can predict intrinsic lifetimes and mean free paths that are hard to extract from experiments due to the presence of impurities and defects in real samples. We can also use our model to directly evaluate the influence of defects and impurities.”

Neaton, like Louie, is a senior MSD faculty scientist with the University of California (UC) Berkeley. Neaton also holds an appointment with the Kavli Institute for Energy Nanosciences. They are the corresponding authors of a paper in Physical Review Letters describing this work titled “Ab Initio Study of Hot Carriers in the First Picosecond after Sunlight Absorption in Silicon.” Bernardi is the lead author of the paper, and Vigil-Fowler the primary coauthor.

Single-junction solar cells based on crystalline silicon are rapidly approaching the theoretical limit of their efficiency, which is approximately 30-percent. This means that if a silicon-based solar cell collects 1,000 Watts per square meter of energy, the most electricity it can generate is 300 Watts per square meter. Hot carriers are crucial to enhancing solar cell  efficiency, since their thermalization results in the loss of as much as a third of the absorbed solar energy in silicon, and similar values in other semiconductors. However, the properties of hot carriers in complex materials for photovoltaic and other modern optoelectronic applications are still poorly understood.

“Our study was aimed at providing useful data for hot carrier dynamics in silicon with application in solar cells,” says Bernardi. “In this study we provide calculations from first principles that describe the two key loss mechanisms, induced by electrons and phonons, respectively, with state-of-the-art accuracy and within the frameworks of density functional and many-body perturbation theories.”

When the research team applied their method to study the relaxation time and mean free path of hot carriers in silicon, they found that thermalization under solar illumination is completed within 350 femtoseconds, and is dominated by phonon emission from hot carriers, a process that becomes progressively slower as the hot carriers lose energy and relax toward the band edges. This modeling result was in excellent agreement with the results of pump-probe experiments. While the model was only tested on silicon in this study, the researchers are confident it will be equally successful with other materials.

“We believe our approach is highly valuable to experimental groups studying hot carriers in the context of solar cells and other renewable energy technologies as it can be used to compute the lifetime and mean free path of hot carriers with specific energies, momenta, and crystallographic directions with unprecedented resolution,” Bernardi says. “As we expand our study of hot carriers to a range of crystalline materials and nanostructures, we believe that our data will provide unique microscopic insight to guide new experiments on hot carriers in semiconductors.”

This research was supported by the DOE Office of Science and the National Science Foundation and made use of the Molecular Foundry, as well as computational resources of the National Energy Research Scientific Computing Center (NERSC), which is also supported by the DOE Office of Science.

Additional Information

For more about the research of Steven Louie go here

For more about the research of Jeff Neaton go here

For more about the Molecular Foundry go here

For more about NERSC go here

For more about the Kavli Institute for Energy Nanosciences go here

– See more at: http://newscenter.lbl.gov/2014/07/17/first-ab-initio-method-for-characterizing-hot-carriers/#sthash.wY178h9s.dpuf

Progress Review of the National Nanotechnology Initiative: Update


3D rendered Molecule (Abstract) with Clipping PathThis document provides an overview of progress on the implementation and coordination of the 2011 NNI Environmental, Health, and Safety (EHS) Research Strategy that was developed by the Nanoscale Science, Engineering, and Technology Subcommittee’s Nanotechnology Environmental and Health Implications (NEHI) Working Group.

 

Consistent with the adaptive management process described in this strategy, the NEHI Working Group has made significant progress through the use of various evaluation tools to understand the current status of nanotechnology-related EHS (nanoEHS) research and the Federal nanoEHS research investment.

Most notably, the participating agencies reported to the NEHI Working Group examples of ongoing, completed, and anticipated EHS research (from FY 2009 through FY 2012) relevant to implementation of the 2011 NNI EHS Research Strategy.

These examples, described in this document, demonstrate the breadth of activities in all six core research areas of the 2011 NNI EHS Research Strategy: Nanomaterial Measurement Infrastructure, Human Exposure Assessment, Human Health, Environment, Risk Assessment and Risk Management Methods, and Informatics and Modeling. Overall, coordination and implementation of the 2011 NNI EHS Strategy across the NEHI agencies has enabled:

  • Development of comprehensive measurement tools that consider the full life cycles of engineered nanomaterials (ENMs) in various media.
  • Collection of exposure assessment data and resources to inform workplace exposure control strategies for key classes of ENMs.
  • Enhanced understanding of the modes of interaction between ENMs and physiological systems relevant to human biology.
  • Improved assessment of transport and transformations of ENMs in various environmental media, biological systems, and over full life cycles.
  • Development of principles for establishing robust risk assessment and risk management practices for ENMs and nanotechnology-enabled products that incorporate ENMs, as well as approaches for identifying, characterizing, and communicating risks to all stakeholders.
  • Coordination of efforts to enhance data quality, modeling, and simulation capabilities for nanotechnology, towards building a collaborative nanoinformatics infrastructure.

Extensive collaboration and coordination among the NEHI agencies as well as with international organizations is evident by the numerous research examples and by other activities such as co-sponsored workshops and interagency agreements described in this review document. These examples and activities are a small subset of the extensive research efforts at the NEHI agencies. This document addresses the NEHI Working Group’s broader efforts in coordination, implementation, and social outreach in nanoEHS, as identified in the 2011 NNI EHS Research Strategy. As the NNI agencies sustain a robust budget for EHS research, Federal agencies will continue to invest in tools and share information essential to assess and manage potential risks of current and anticipated ENMs and nanotechnology-enabled products throughout their life cycles. The agencies will also continue to engage with the stakeholder community to establish a broad EHS knowledge base in support of regulatory decision making and responsible development of nanotechnology.

 

A Google Glass app for instant medical diagnostics (w/video)


(Nanowerk Spotlight)  By Michael Berger. Copyright © Nanowerk

2x2-logo-sm.jpgThe integration of consumer electronics with advanced imaging and analytical platforms holds great promises for medical point-of-care diagnostics and environmental rapid field testing for pollutants and viruses. For instance, in a recent Nanowerk Spotlight we reported on the use of smartphones to detect single nanoparticles and viruses.

In this work, a research group led by Aydogan Ozcan, a professor in the Electrical and Bioengineering Department at UCLA and Associate Director of the California NanoSystems Institute (CNSI), created a field-portable fluorescence microscopy platform installed on a smartphone for imaging of individual nanoparticles as well as viruses using a light-weight and compact opto-mechanical attachment to the existing camera module of the cellphone.

“This technology allows Google Glass wearers to use the hands-free camera on the device to send images of diagnostic tests that screen for conditions such as HIV or prostate cancer,” Ozcan explains to Nanowerk. “Without relying on any additional devices, Google Glass users can upload these images and receive accurate analysis of health conditions in as little as eight seconds.”

     Labeled Google Glass and demonstration of imaging a rapid diagnostic test

Labeled Google Glass and demonstration of imaging a rapid diagnostic test (RDT). (a) Front-profile view of the Google Glass with various hardware components36 labeled. (b) Example of using the Glass for taking an image of an RDT as part of our RDT reader application. (Reprinted with permission from American Chemical Society) (click image to enlarge)

This is the first biomedical sensing application created through Google Glass. This breakthrough technology takes advantage of gains in both immunochromatographic rapid diagnostic tests (RDTs) and wearable computers (such as Google Glass). The team reported their findings in  the February 27, 2014 online edition of ACS Nano (“Immunochromatographic Diagnostic Test Analysis Using Google Glass”).

Over the past decade, RDTs – which are in general based on light scattering off surface-functionalized metallic nanoparticles – have emerged as a quick and cost-effective method to screen various diseases and have provided various advantages for tackling public health problems including more effective tracking/monitoring of chronic conditions, infectious diseases and widespread medical testing by minimally trained medical personnel or community healthcare workers.

The new Google Glass-based diagnostic technology could improve individual tracking of dangerous conditions or diseases, public health monitoring and rapid response in disaster relief areas or quarantine zones. This is how it works: The user takes a photo of the RDT device through the camera system in Google Glass. Using a Quick Response (QR) code identifier, which is custom-designed and attached to each RDT cassette, this custom-written Glass application is capable of automatically finding and identifying the type of the RDT of interest, along with other information (e.g., patient data) that can be linked to the same QR code.

The data is transmitted to a central server which has been set up for fast and high-throughput evaluation of test results coming from multiple devices simultaneously. The data is processed automatically and to create a quantitative diagnostic result, which is then returned to the Google Glass user.

Here is how it looks through the screen of Google Glass during imaging and quantification of a diagnostic test.

This is the first biomedical sensing application on Google Glass.
Achieved a few parts per billion level of sensitivity with Glass.

“We also developed a centralized database and Web interface for visualizing uploaded data in the form of geo-tagged map data, which can be quite useful for short- and long-term spatiotemporal tracking of the evolution,” says Ozcan. “This web portal allows users to view test results, maps charting the geographical spread of various diseases and conditions, and the cumulative data from all the tests they have submitted over time.” He also points out that the precision of the Google Glass camera system permits quantified reading of the results to a few-parts-per-billion level of sensitivity – far greater than that of the naked eye – thus eliminating the potential for human error in interpreting results, which is a particular concern if the user is a health care worker who routinely deals with many different types of tests.

         rapid diagnostic test imaging and processing workflow done by the Google Glass application

Block diagram of the rapid diagnostic test (RDT) imaging and processing workflow (a, c) done by the Google Glass application (red dashed frame) and server processes (green dashed frame). In this case, a single RDT is analyzed. (Reprinted with permission from American Chemical Society) (click image to enlarge)

The team tested their Google Glass-based RDT reader platform through commercially available human immunodeficiency virus (HIV) and prostate-specific antigen (PSA) rapid tests. The researchers took images of tests under normal, indoor, fluorescent-lit room conditions. They submitted more than 400 images of the two tests, and the RDT reader and server platform were able to read the images 99.6 percent of the time. Ozcan notes that, for wide-scale deployment and use of this Google Glass application, the sales price of Glass should be cost-effective enough to compete with mobile phones and low enough to enter developing markets.

“We are quite hopeful on this end as Google is very well aware of all these emerging opportunities.”

Read more: A Google Glass app for instant medical diagnostics (w/video) http://www.nanowerk.com/spotlight/spotid=34615.php#ixzz2vIsTVapx

ACS Nano article:    http://pubs.acs.org/doi/abs/10.1021/n…
Created by Ozcan Research Lab at UCLA:

Roots of the Lithium Battery Problem: Berkeley Lab Researchers Find Dendrites Start Below the Surface


carbon-nanotubeThe lithium-ion batteries that power our laptops, smartphones and electric vehicles could have significantly higher energy density if their graphite anodes were to be replaced by lithium metal anodes. Hampering this change, however, has been the so-called dendrite problem. Over the course of several battery charge/discharge cycles, particularly when the battery is cycled at a fast rate, microscopic fibers of lithium, called “dendrites,” sprout from the surface of the lithium electrode and spread like kudzu across the electrolyte until they reach the other electrode. An electrical current passing through these dendrites can short-circuit the battery, causing it to rapidly overheat and in some instances catch fire. Efforts to solve the problem by curtailing dendrite growth have met with limited success, perhaps because they’ve just been scratching the surface of the problem.

These 3D reconstructions show how dendritic structures that can short-circuit a battery form deep within a lithium electrode, break through the surface and spread across the electrolyte.

These 3D reconstructions show how dendritic structures that can short-circuit a battery form deep within a lithium electrode, break through the surface and spread across the electrolyte.

Researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have discovered that during the early stages of development, the bulk of dendrite material lies below the surface of the lithium electrode, underneath the electrode/electrolyte interface. Using X-ray microtomography at Berkeley Lab’s Advanced Light Source (ALS), a team led by Nitash Balsara, a faculty scientist with Berkeley Lab’s Materials Sciences Division, observed the seeds of dendrites forming in lithium anodes and growing out into a polymer electrolyte during cycling. It was not until the advanced stages of development that the bulk of dendrite material was in the electrolyte. Balsara and his colleagues suspect that non-conductive contaminants in the lithium anode trigger dendrite nucleation.

Nitash Balsara and Katherine Harry at ALS beamline 8.3.2 where they shed important new light on the dendrite problem in lithium batteries. (Photo by Roy Kaltschmidt)

Nitash Balsara and Katherine Harry at ALS beamline 8.3.2 where they shed important new light on the dendrite problem in lithium batteries. (Photo by Roy Kaltschmidt)

“Contrary to conventional wisdom, it seems that preventing dendrite formation in polymer electrolytes depends on inhibiting the formation of subsurface dendritic structures in the lithium electrode,” Balsara says. “In showing that dendrites are not simple protrusions emanating from the lithium electrode surface and that subsurface non-conductive contaminants might be the source of dendritic structures, our results provide a clear prescription for the path forward to enabling the widespread use of lithium anodes.”

Balsara, who is a professor of chemical engineering at the University of California (UC) Berkeley, is the corresponding author of a paper describing this research in Nature Materials titled “Detection of subsurface structures underneath dendrites formed on cycled lithium metal electrodes.” Co-authors are Katherine Harry, Daniel Hallinan, Dilworth Parkinson and, Alastair MacDowell.

The tremendous capacity of lithium and the metal’s remarkable ability to move lithium ions and electrodes in and out of an electrode as it cycles through charge/discharge make it an ideal anode material. Until now, researchers have studied the dendrite problem using various forms of electron microscopy. This is the first study to employ microtomography using monochromatic beams of high energy or “hard” X-rays, ranging from 22 to 25 keV, at  ALS beamline 8.3.2. This technique allows non-destructive three-dimensional imaging of solid objects at a resolution of approximately one micron.

“We observed crystalline contaminants in the lithium anode that appeared at the base of every dendrite as a bright speck,” says Katherine Harry, a member of Balsara’s research group and the lead author of the Nature Materials paper. “The lithium foils we used in this study contained a number of elements other than lithium with the most abundant being nitrogen. We can’t say definitively that these contaminants are responsible for dendrite nucleation but we plan to address this issue by conducting in situ X-ray microtomography.”

Balsara and his group also plan further study of the role played by the electrolyte in dendrite growth, and they have begun to investigate ways to eliminate non-conductive impurities from lithium anodes.

This research was funded by the DOE Office of Science.

Tetrapod Quantum Dots Light the Way to Stronger Polymers


Berkeley Lab Researchers Use Fluorescent Tetrapod Quantum Dots to Measure the Mechanical Strength of Polymer Fibers

qdot-images-3.jpgFluorescent tetrapod nanocrystals could light the way to the future design of stronger polymer nanocomposites. A team of researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) has developed an advanced opto-mechanical sensing technique based on tetrapod quantum dots that allows precise measurement of the tensile  strength of polymer fibers with minimal impact on the fiber’s mechanical properties.

In a study led by Paul Alivisatos, Berkeley Lab director and the Larry and Diane Bock Professor of Nanotechnology at the University of California (UC) Berkeley, the research team incorporated into polymer fibers a population of tetrapod quantum dots (tQDs) consisting of a cadmium-selenide (CdSe) core and four cadmium sulfide (CdS) arms. The tQDs were incorporated into the polymer fibers via electrospinning, among today’s leading techniques for processing polymers, in which a large electric field is applied to droplets of polymer solution to create micro- and nano-sized fibers. This is the first known application of electrospinning to tQDs.

 

Fluorescent tetrapod quantum dots or tQDs (brown) serve as stress probes that allow precise measurement of polymer fiber tensile strength with minimal impact on mechanical properties. Inserts show relaxed tQDs (upper) and stressed tQDs (lower).

“The electrospinning process allowed us to put an enormous amount of tQDs, up to 20-percent by weight, into the fibers with minimal effects on the polymer’s bulk mechanical properties,” Alivisatos says. “The tQDs are capable of fluorescently monitoring not only simple uniaxial stress, but stress relaxation and behavior under cyclic varying loads. Furthermore, the tQDs are elastic and recoverable, and undergo no permanent change in sensing ability even upon many cycles of loading to failure.”

Alivisatos is the corresponding author of a paper describing this research in the journal NANO Letters titledTetrapod Nanocrystals as Fluorescent Stress Probes of Electrospun Nanocomposites.” Coauthors were Shilpa Raja, Andrew Olson, Kari Thorkelsson, Andrew Luong, Lillian Hsueh, Guoqing Chang, Bernd Gludovatz, Liwei Lin, Ting Xu and Robert Ritchie.

From left, Andrew Olson, Shilpa Raja and Andrew Luong are members of Paul Alivisatos's research group who used electrospinning to incorporate tetrapod quantum dot stress probes into polymer fibers. (Photo by Roy Kaltschmidt)

From left, Andrew Olson, Shilpa Raja and Andrew Luong are members of Paul Alivisatos’s research group who used electrospinning to incorporate tetrapod quantum dot stress probes into polymer fibers. (Photo by Roy Kaltschmidt)

Polymer nanocomposites are polymers that contain fillers of nanoparticles dispersed throughout the polymer matrix. Exhibiting a wide range of enhanced mechanical properties, these materials have great potential for a broad range of biomedical and material applications. However, rational design has been hampered by a lack of detailed understanding of how they respond to stress at the micro- and nanoscale.

“Understanding the interface between the polymer and the nanofiller and how stresses are transferred across that barrier are critical in reproducibly synthesizing composites,” Alivisatos says. “All of the established techniques for providing this information have drawbacks, including altering the molecular-level composition and structure of the polymer and potentially weakening mechanical properties such as toughness. It has therefore been of considerable interest to develop optical luminescent stress-sensing nanoparticles and  find a way to embed them inside polymer fibers with minimal impact on the mechanical properties that are being sensed.”

The Berkeley Lab researchers met this challenge by combining semiconductor tQDs of CdSe/CdS, which were developed in an earlier study by Alivisatos and his research group, with electrospinning. The CdSe/CdS tQDs are exceptionally well-suited as nanoscale stress sensors because an applied stress will bend the arms of the tetrapods, causing a shift in the color of their fluorescence. The large electric field used in electrospinning results in a uniform dispersal of tQD aggregates throughout the polymer matrix, thereby minimizing the formation of stress concentrations that would act to degrade the mechanical properties of the polymer. Electrospinning also provided a much stronger bond between the polymer fibers and the tQDs than a previous diffusion-based technique for using tQDs as stress probes that was reported two years ago by Alivisatos and his group. Much higher concentrations of tQDs could also be a achieved with electrospinning rather than diffusion.

When stress was applied to the polymer nanocomposites, elastic and plastic regions of deformation were easily observed as a shift in the fluorescence of the tQDs even at low particle concentrations. As particle concentrations were increased, a  greater fluorescence shift per unit strain was observed. The tQDs acted as non-perturbing probes that tests proved were not adversely affecting the mechanical properties of the polymer fibers in any significant way.

“We performed mechanical tests using a traditional tensile testing machine with all of our types of polymer fibers,” says Shilpa Raja, a lead author of the Nano Letters paper along with Andrew Olson, both members of Alivisatos’ research group. “While the tQDs undoubtedly change the composition of the fiber – it is no longer pure polylactic acid but instead a composite – we found that the mechanical properties of the composite and crystallinity of the polymer phase show minimal change.”

The research team believes their tQD probes should prove valuable for a variety of biological, imaging and materials engineering applications.

“A big advantage in the development of new polymer nanocomposites would be to use tQDs to monitor stress build-ups prior to material failure to see how the material was failing before it actually broke apart,” says co-lead author Olson. “The tQDs could also help in the development of new smart materials by providing insight into why a composite either never exhibited a desired nanoparticle property or stopped exhibiting it during deformation from normal usage.”

For biological applications, the tQD is responsive to forces on the nanoNewton scale, which is the amount of force exerted by living cells as they move around within the body. A prime example of this is metastasizing cancer cells that move through the surrounding extracellular matrix. Other cells that exert force include the fibroblasts that help repair wounds, and cardiomyocytes, the muscle cells in the heart that beat.

“All of these types of cells are known to exert nanoNewton forces, but it is very difficult to measure them,” Raja says.

“We’ve done preliminary studies in which we have shown that cardiomyocytes on top of a layer of tQDs can be induced to beat and the tQD layer will show fluorescent shifts in places where the cells are beating. This could be extended to a more biologically-relevant environment in order to study the effects of chemicals and drugs on the metastasis of cancer cells.”

Another exciting potential application is the use of tQDs to make smart polymer nanocomposites that can sense when they have cracks or are about to fracture and can strengthen themselves in response.

“With our technique we are combining two fields that are usually separate and have never been combined on the nanoscale, optical sensing and polymer nanocomposite mechanical tunability,” Raja says. “As the tetrapods are incredibly strong, orders of magnitude stronger than typical polymers, ultimately they can make for stronger interfaces that can self-report impending fracture.”

This research was primarily supported by the DOE Office of Science.

#  #  #

Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit www.lbl.gov.

DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit the Office of Science website at science.energy.gov/.

 

Additional Information

For more about the research of Paul Alivisatos go here

%d bloggers like this: